St. Louis O'Fallon St. Charles St. Peters Wentzville In popular culture In The Simpsons episode "A Tale of Two Springfields" which first aired on November 5, 2000, 636 is one of two area codes (the other being 939) assigned to the fictional town of Springfield. See also List of exchanges from AreaCodeDownload.com, 636 Area Code References 636 636 Telecommunications-related introductions in 1999